1. Field of the Invention
The present invention relates generally to measurement tools, and particularly to a non-contact measurement probe that measures the diameter and roundness of a workpiece while being machined in a computer numerical controlled (CNC) machine.
2. Description of the Related Art
Zero defect parts can only be obtained via full automatic error compensation while they are being machined on the next generation of intelligent machining processes to ensure high quality products at low price in a short period of time. Off-line axis error compensation is successfully achieved with NC machines including thermal sensors, while on-line compensation still has some difficulties, mainly with probes, hardware, and controllers. Quality control of manufactured parts is traditionally performed using manual inspection methods and statistical sampling procedures. It has the disadvantages of releasing some defective parts and requiring an inspection area. To overcome these problems, in-process inspection with error correction in NC machines is proposed as another alternative.
In-process measurement techniques have been proposed over the last two decades to control the quality of a workpiece, with some difficulties to be addressed. The principal trend in this type of inspection is to use a measuring probe with a measurement control system and to adjust machining parameters to reach the nominal dimension with the required accuracy. Optical measurement techniques have the advantage of being fast and non-contact.
A variety of optical sensors are applied to measurement in metrology. The most common techniques include triangulation, shearing interference, coherence radar, and laser Doppler techniques. Laser Doppler Velocimetry has proven to be very accurate and repeatable for many years for fluid applications, such as anemometry. Also, laser Doppler systems find application in length measurement of sheet materials (e.g., paper, textiles and foils). Recently, an indirect measurement method for the determination of surface velocity in vibrating structures based on laser-Doppler vibrometry has been investigated.
In mass production, diameter is one of the significant parameters to be inspected. Many measurement techniques have been developed to measure the diameter of a workpiece. It would be desirable to have an in-process laser-Doppler technique that could measure the diameter of a moving workpiece.
Thus, a non-contact measurement probe solving the aforementioned problems is desired.